docs: def pixels_to_ndc(pos, size=None):
      """Convert from pixels to normalized device coordinates (in [-1, 1])."""
      pos = np.asarray(pos, dtype=np.float64)
      size = np.asarray(size, dtype=np.float64)
      pos = pos / (size / 2.) - 1
      # Flip y, because the origin in pixels is at the top left corner of the
      # window.
      pos[1] = -pos[1]
      return pos